1. Technical Field of the Invention
The present invention relates to a method for fabricating a liquid crystal display device, and more particularly, to a method for fabricating a CF (color filter) on a TFT (thin-film transistor) liquid crystal display device in which switching elements and color filters of a plurality of colors are formed on the same transparent substrate.
2. Description of the Related Art
In some color twisted nematic (TN) liquid crystal display devices having TFTs, color filters are provided on a counter substrate opposed to the TFT substrate where TFTs are provided. In forming the counter substrate for such liquid crystal display devices, material films of color filters of three colors containing a thermosetting resin are printed onto the transparent substrate, thereafter, the material films are hardened by being heated, thereby forming the color filters. This fabricating method is described, for example, in Japanese Unexamined Patent Publication Hei-4-369605. Then, the TFT substrate and the counter substrate are bonded together to form a liquid crystal display panel.
FIG. 1 is a cross-sectional view showing the positional relationship between the TFT substrate and the counter substrate in a conventional liquid crystal display device. In the conventional liquid crystal display device, a liquid crystal layer 230 is provided between first and second transparent substrates 201 and 223. Hereinafter, the liquid crystal layer 230 side of the first and the second transparent substrates 201 and 223 will be referred to as the inner side, and the side opposite thereto, as the outer side.
On the inside surface of the first transparent substrate 201, gate electrodes 203 connected to scanning lines (not shown) are formed, and a gate insulating film 204 is formed so as to cover the gate electrodes 203. In the positions on the gate insulating film 204 corresponding to the gate electrodes 203, semiconductor layers 205 are formed, and drain electrodes 207 and source electrodes 208 are formed so as to sandwich the semiconductor layers 205. Further, a passivation film 209 is formed so as to cover them, and pixel electrodes 216 connected to the source electrodes 208 pixel by pixel through contact holes (not shown) formed in the passivation film 209 are formed on the passivation film 209. On the pixel electrodes 216, an alignment film 217 is formed.
On the inside surface of the second transparent substrate 223, a black matrix 212, color filters 210 of each color, a transparent common electrode 221 and an alignment film 222 are provided in succession.
In a case where the conventional liquid crystal display device in which such color filters are provided on the counter substrate is fabricated, when the TFT substrate and the counter substrate are bonded together, a position shift sometimes occurs between the region on the TFT substrate that is partitioned by the scanning lines and the data lines and in which the pixel electrodes 216 are provided, and the region on the counter substrate that is partitioned by the black matrix and in which the color filters are provided. When such a position shift occurs, colors come out in positions where no color is expected to come out in design, so that desired color development is not obtained. For this reason, it is necessary to provide between pixels a margin for compensating for the position shift, that is, a black matrix larger than the theoretical value, so that it is difficult to obtain pixels of a sufficient area. Consequently, sufficient luminance cannot be obtained. This defect becomes more conspicuous as the pitch between pixels decreases with improvement in resolution.
Therefore, recently, a liquid crystal display device in which color filters are provided on the TFT substrate has been developed, and this substrate is called a CF on a TFT substrate (Japanese Unexamined Patent Publication 2000-231123).
A method for fabricating a conventional CF on a TFT substrate will be described. FIG. 2 through FIG. 11 are cross-sectional views showing the method for fabricating the conventional CF on a TFT substrate in order in which the fabricating steps are performed.
In the method for fabricating the conventional CF on a TFT substrate, first, scanning lines 102 and gate electrodes (not shown) are selectively formed on a transparent substrate 101, and as shown in FIG. 2, a gate insulating film 104 is formed on the entire surface. Then, semiconductor layers (not shown), data lines 106, drain electrodes (not shown) and source electrodes 108 are formed on the gate insulating film 104, and further, a passivation film 109 is formed on the entire surface. By this step, a TFT is formed in each pixel. Further, a red negative photosensitive resin film 110Ra is formed on the passivation film 109 by spin coating. The viscosity of the photosensitive resin film 110Ra is approximately 10 (mPa.S).
Then, as shown in FIG. 3, the photosensitive resin film 110Ra is exposed by use of a photomask 111R intercepting light for the regions other than the pixels for red and the regions of the pixels for red where contact holes for connecting the transparent pixel electrodes and the source electrodes 108 are to be formed.
Then, the photosensitive resin film 110Ra is developed. Since the photosensitive resin film 110Ra is negative, the regions of the photosensitive resin film 110Ra corresponding to the light-intercepted regions, that is, the regions other than the pixels for red and the regions having the pixels for red where the contact holes for connecting the transparent pixel electrodes and the source electrodes 108 are to be formed are removed by the development as shown in FIG. 4, so that color filters 110R are formed.
Then, as shown in FIG. 5, a green negative photosensitive region film 110Ga is formed on the entire surface by spin coating. The viscosity of the photosensitive resin film 110Ga is also approximately 10 (mPa.s).
Then, as shown in FIG. 6, the photosensitive resin film 110Ga is exposed by use of a photomask 111G intercepting light for the regions other than the pixels for green and the regions of the pixels for green where contact holes for connecting the transparent pixel electrodes and the source electrodes 108 are to be formed.
Then, as shown in FIG. 7, the photosensitive resin film 110Ga is developed. Since the photosensitive resin film 110Ga is negative, the regions of the photosensitive resin film 110Ga corresponding to the light-intercepted regions are removed by the development, so that color filters 110G are formed.
Then, as shown in FIG. 8, a blue negative photosensitive region film 110Ba is formed on the entire surface by spin coating. The viscosity of the photosensitive resin film 110Ba is also approximately 10 (mPa.s).
Then, as shown in FIG. 9, the photosensitive resin film 110Ba is exposed by use of a photomask 111B intercepting light for the regions other than the pixels for blue and the regions of the pixels for blue where contact holes for connecting the transparent pixel electrodes and the source electrodes 108 are to be formed.
Then, the photosensitive resin film 110Ba is developed. Since the photosensitive resin film 110Ba is negative, the regions of the photosensitive resin film 110Ba corresponding to the light-intercepted regions are removed by the development as shown in FIG. 10, so that color filters 110B are formed.
Then, as shown in FIG. 11, a black matrix 112 is formed in the regions corresponding to the TFTs, and the scanning lines and the data lines 106 on the color filters. Further, an overcoat layer 113 is formed on the black matrix 112, and an overcoat layer 114 having openings 114a in the openings of the color filters 10R, 110G and 10B is formed. Then, openings 109a are formed in the regions of the passivation film 109 exposed in the openings 114a. Contact holes 115 reaching the source electrodes 108 from the openings 109a and 114a are structured. Then, transparent pixel electrodes 116 connected to the source electrodes 108 through the contact holes 115 pixel by pixel are formed on the overcoat layer 114. Then, an alignment film (not shown) is formed on the transparent pixel electrodes 116. In this manner, the CF on a TFT substrate is fabricated.
However, when the CF on a TFT substrate is fabricated by this method, the necessity for application of the photosensitive resist film and the exposure and development color by color increases the number of fabricating steps. In addition, since the photosensitive resist film is applied to the entire surface of the transparent substrate, that is, since the photosensitive resist film is applied also to pixels not requiring the application of the photosensitive resist film, the amount of photosensitive resist film removed by the succeeding exposure and development is extremely large, which increases the manufacturing cost more than necessary.
Therefore, it is considered to apply printing as described above using a thermosetting resin, to form color filters on the CP on a TFT substrate. However, when printing is used, since the current printing machines are not high in precision, alignment precision as high as that of photolithography cannot be obtained. In the conventional liquid crystal display devices in which the color filters are provided on the counter substrate, since it is necessary only that the color filters can be formed in the region partitioned by the black matrix, particularly high alignment precision is not required. However, in the case of the CF on a TFT substrate, since the color filters are present between the source electrodes and the pixel electrodes, openings are required for color filters, so that extremely high alignment precision is required. That is, when the alignment precision on the CF on a TFT substrate is low, a position shift of the openings occurs, so that excellent images cannot be obtained due to variations in resistance. Therefore, it is impossible to simply divert the conventional printing to the fabrication of the CF on a TFT substrate.
An object of the present invention is to provide a method for fabricating a liquid crystal display device capable of reducing the number of fabricating steps while ensuring high alignment precision, preferably, capable of reducing the consumption amount of the material.
A method for fabricating a liquid crystal display device according to the present invention comprises the steps of: forming a switching element for each pixel on a transparent substrate; forming color filters of a plurality of colors on the transparent substrate so that the color filters cover the switching elements; simultaneously forming an opening reaching a predetermined electrode of each of the switching elements, in each of the color filters for all colors; and forming, on each of the color filters, a pixel electrode connected to the predetermined electrode through the opening.
According to the present invention, since after the color filters are formed, the formation of the openings in the color filters is simultaneously performed on the color filters for all colors, a reduction in alignment precision occurring when printing is adopted can be avoided. In addition, since it is unnecessary to perform the formation of the openings color by color, the number of fabricating steps can be reduced to improve productivity.
In forming of the color filters of the plurality of colors, by printing materials of the color filters each colored in a predetermined color onto the transparent substrate, the color filters of the plurality of colors can be easily formed.
In the forming of the color filters of the plurality of colors, the color filters for all colors are preferable to be simultaneously formed. Thereby, it is unnecessary to apply the color filters color by color, so that the number of fabricating steps can be further reduced.
By using a photosensitive resist film as the materials of the color filters, photolithography can be adopted for the formation of the openings, so that the openings can be formed with high precision. Consequently, the forming of the openings can have the steps of: exposing the color filters of the plurality of colors by use of a photomask intercepting light for positions corresponding to the predetermined electrodes; and developing the color filters of the plurality of colors.
Another method according to the present invention is a method for fabricating a liquid crystal display device in which switching elements and color filters of a plurality of colors are formed on the same transparent substrate. The method comprises the steps of simultaneously printing, onto the transparent substrate, the color filters for all colors consisting of a photosensitive resist film; exposing the color filters of the plurality of colors by use of a photomask intercepting light for positions corresponding to predetermined electrodes of the switching elements; and developing the color filters of the plurality of colors.
According to the present invention, improvement in productivity because of a reduction in the number of fabricating steps, and a reduction in the consumption amount of the material are achieved, and high alignment precision is ensured in the formation of the openings.